Sheet piling material, or sheet piling, is used to form continuous earth retaining walls or sea walls. Some of the uses of such walls include anchored bulkheads, shore-protection walls, soil retaining walls, water-control structures, cut-off walls to control ground water or hazardous chemical seepage, and trenching. The retaining walls or sea walls are typically formed by driving the elongated, planar sheet piling material vertically into the ground, with adjacent sheets being joined to each other to form a sturdy structure. The sheets are typically driven into the ground by pile driving, and the sheets must have sufficient stiffness to withstand the pile driver without buckling or otherwise failing.
Usually, the sheet piling material has a panel side edge configuration that enables interlocking of the panel edges with the edge of an adjacent panel. Sheet pilings can be made of many different types of material, including steel, aluminum, treated timber, extruded vinyl sheet material, and fiber-reinforced pultruded polymer material. Sheet pilings are used in different cross-sectional configurations, such as Z-shaped, U-shaped, and arch-shaped configurations, as well as a straight flat configuration. There are currently more than ten US-based and international steel sheet piling manufacturers who produce nearly 200 different sheet piling configurations.
Steel pilings are widely used for sheet piling material due to the superior strength and ductility of steel, the efficient use of the material in various cross-sectional configurations, and the ease of installation due to interlocking. However, there are two major drawbacks to using steel: corrosion and high weight. An alternative to steel is aluminum. While more corrosion-resistant than steel, aluminum sheet pilings are more expensive than steel. Another choice for sheet pilings is preservative-treated timber. While timber retaining structures are less expensive than metallic systems, they are coming under increased environmental scrutiny because of the preservatives used in the timber. Extruded vinyl sheet pilings can also be used for sheet pilings. The vinyl pilings are more durable that either the steel or the wood pilings, but they are expensive and suffer problems related to low strength and low stiffness. Pultruded fiber-reinforced polymer sheet pilings are stronger and stiffer than their extruded counterparts, but are more expensive.
The predominantly-used steel piles are typically made using hot rolling or cold forming, although other methods can be used. Hot rolled panels are produced by a steel hot-mill procedure in which the shape is reduced during a series of rolling stages to the final form. The thickness of flanges and webs can be adjusted and interlocks that connect one sheet pile to the other are shaped by the flow of hot metal. The shape of cold formed sheet piles is obtained by passing cold sheet steel through a series of rolls. The interlock is formed, for example, by bending the flange ends into a hook-and-grip cross-sectional configuration or a male-female ball and socket joint configuration. While there is no standard interlock design, interlocks are usually designed to provide a permanent connection of individual sheets in order to form a continuous, relatively water-tight or earth-tight wall, and to allow reasonably free sliding to facilitate installation. Also, the sheet piling material is designed to provide adequate pull strength in applications where the sheet material is under tension, and to provide a certain amount of swing.
It would be advantageous if there could be developed an improved sheet piling material, taking into consideration such factors as structural strength requirements, cost, ease of installation, durability, and absence of environmental problems.